21216980 has 48 divisors (see below), whose sum is σ = 46584720. Its totient is φ = 8107008.

The previous prime is 21216961. The next prime is 21216983. The reversal of 21216980 is 8961212.

It can be written as a sum of positive squares in 8 ways, for example, as 2155024 + 19061956 = 1468^2 + 4366^2 .

It is a Harshad number since it is a multiple of its sum of digits (29).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216983) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 90944 + ... + 91176.

It is an arithmetic number, because the mean of its divisors is an integer number (970515).

Almost surely, 2^21216980 is an apocalyptic number.

21216980 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21216980, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23292360).

21216980 is an abundant number, since it is smaller than the sum of its proper divisors (25367740).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21216980 is a wasteful number, since it uses less digits than its factorization.

21216980 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 428 (or 426 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 29.

The square root of 21216980 is about 4606.1893143899. The cubic root of 21216980 is about 276.8393721768.

The spelling of 21216980 in words is "twenty-one million, two hundred sixteen thousand, nine hundred eighty".